Method for producing honeycomb structures

ABSTRACT

A plurality of inlet-side octagonal cells and outlet-side quadrangular cells partitioned by partition walls on an upper surface and a lower surface are opened in a green honeycomb molded body in which a plurality of through-holes partitioned from each other by the partition walls are open in an end surface of a columnar body. Four outlet-side quadrangular cells having a smaller opening area adjoin around one inlet-side octagonal cell through the partition walls. The partition walls are joined together and the inlet-side octagonal cells are opened while closing the outlet-side quadrangular cells on the inlet side and the outlet-side quadrangular cells are opened while closing the inlet-side octagonal cells on the outlet side in a particulate-matter-removing filter such as a diesel particulate filter.

TECHNICAL FIELD

An aspect of the present invention relates to a method for producinghoneycomb structures and also relates to a method for producinghoneycomb structures in which a green honeycomb molded body is fired toproduce a honeycomb structure.

BACKGROUND ART

For example, honeycomb hole structures made of ceramic and having aplurality of through-holes of a cross-section polygonal shape areconventionally known. Such honeycomb structures are used, for example,in particulate-matter-removing filters such as diesel particulatefilters. In a production step of such honeycomb structures, a ceramicraw material powder is formed by extruding to produce a green honeycombmolded body. A part of through-holes in this green honeycomb molded bodyare closed at an end surface. A honeycomb structure is produced byfiring the green honeycomb molded body with closed through-holes. PatentLiterature 1 discloses a method for producing such honeycomb structures.In Patent Literature 1, a sealing material is pressed with a pistonagainst one end of a honeycomb structure placed within a cylinder tosupply the sealing material to the end of through-holes in the honeycombstructure and to close the through-holes.

CITATION LIST Patent Literature

-   PTL 1: Japanese Examined Patent Publication No. S63-24731

SUMMARY OF INVENTION Technical Problem

However, in the method in the above Patent Literature 1, sealingmaterials such as sealing pastes are necessary. Further, PatentLiterature 1 has the problem that it requires a very troublesome step,for example, applying a sealing mask to an end surface and opening ahole at a place to be closed in the mask.

In the technical field, production methods in which sealing pastes arenot needed and which can simply close the end of a honeycomb structure,and honeycomb structures obtained by those production methods have beendesired.

Solution to Problem

One aspect of the present invention is a method for producing ahoneycomb structure, the method comprising a closing step of joiningtogether partition walls of a green honeycomb molded body in which aplurality of through-holes partitioned by partition walls are open toeach other at the end surface of a columnar body to close a part of thethrough-holes, wherein the green honeycomb molded body in which a partof the through-holes are closed at the closing step includes, at the endsurface, one first through-hole and four second through-holes that havea smaller opening area than the first through hole and that adjoinaround the first through-hole with the partition wall provided betweenthe first through-hole and the second through-holes.

With this construction, it is unnecessary to use sealing pastes, such asin conventional methods, and the end of honeycomb structures can besimply closed. Further, since cells are closed by welding cell wallstogether, when the honeycomb structure is used in diesel particulatefilters, turbulence of flow of exhaust gases at the end surface on theexhaust gas supply side is reduced and pressure loss can be reduced.

In this case, the first through-hole may be octagonal, and the secondthrough-holes may be quadrangular.

According to this construction, the first through-hole is octagonal, andthe second through-holes are quadrangular. For this reason, for example,when the quadrangular through-holes adjoin every other side of theoctagonal through-hole, through-holes having a different size can bearranged in the end surface.

Further, the first through-hole may have a round quadrangular shape witha corner of the quadrangle being rounded, and the second through-holemay have a quadrangular shape.

According to this construction, the first through-hole has a roundquadrangular shape with the corner of the quadrangle being rounded, andthe second through-hole has a quadrangular shape. For this reason, forexample, when the quadrangular through-hole adjoins each of the foursides of the round quadrangular through-hole, through-holes having adifferent size can be arranged in the end surface.

Further, at the closing step, the second through-hole can be closed atone of the end surfaces and the first through-hole can be closed at theother end surface.

According to this construction, at the closing step, the secondthrough-holes are closed at one of the end surfaces, and the firstthrough-holes are closed at the other end surface. For this reason, forexample, when the honeycomb structure is applied to aparticulate-matter-removing filter such as a diesel particulate filter,when first through-holes having a large opening area are open whileclosing the second through-holes having a small opening area on an inletside of the particulate-matter-removing filter, and the secondthrough-holes having a small opening area are open while closing thefirst through-holes having a large opening area on an outlet side, theinlet side becomes wide and pressure loss in a state in which soot isdeposited can be reduced.

Further, at the closing step, by inserting a closing tool into a part ofa plurality of through-holes in the green honeycomb molded body,partition walls are joined together at the end surface and thethrough-holes can be closed.

According to this construction, at the closing step, by inserting aclosing tool into a part of the plurality of through-holes in the greenhoneycomb molded body, the partition walls are joined together at theend surface to close the through-holes. Thus, the closing of thethrough-holes can very easily be carried out.

In this case, at the closing step, in closing the second through-holes,by inserting a closing tool including any one shape of a quadrangularpyramid and a quadrangular pyramid platform into the first through-holewhile allowing the lateral edge of the closing tool to abut against eachof the partition walls that adjoin the second through-holes, the secondthrough-holes can be closed.

According to this construction, at the closing step, in closing thesecond through-holes, by inserting a closing tool including any oneshape of a quadrangular pyramid and a quadrangular pyramid platform intothe first through-hole while allowing the lateral edge of the closingtool to abut against each of the partition walls that adjoin the secondthrough-holes, the second through-holes are closed. Thus, the secondthrough-holes can easily and reliably be closed.

Further, at the closing step, in closing the first through-hole, byinserting a closing tool including any one shape of a quadrangularpyramid and a quadrangular pyramid platform into each of the secondthrough-holes while allowing the lateral edge of the closing tool toabut against the partition walls that adjoin the first through-hole, thefirst through-hole can be closed.

According to this construction, at the closing step, in closing thefirst through-hole, by inserting a closing tool including any one shapeof a quadrangular pyramid and a quadrangular pyramid platform into eachof the second through-holes while allowing the lateral edge of theclosing tool to abut against the partition walls that adjoin the firstthrough-hole, the first through-hole is closed. Thus, the firstthrough-hole can easily and reliably be closed.

Advantageous Effects of Invention

The method for producing a honeycomb structure according to one aspectof the present invention can provide a production method in which asealing paste is not needed and which can simply close the end of thehoneycomb structure, and a honeycomb structure produced by the method.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1(a) is a perspective view of a green honeycomb molded bodyaccording to a first embodiment before closing.

FIG. 1(b) is a partial enlarged view of FIG. 1(a).

FIG. 2 is a perspective view of a closing apparatus for a greenhoneycomb molded body according to a first embodiment.

FIG. 3 is a partial cross-sectional view of a closing tool for an inletside of a green honeycomb molded body according to a first embodiment.

FIG. 4 is an enlarged perspective view of a portion A of FIG. 3.

FIG. 5 is an enlarged plan view of a portion A of FIG. 3.

FIG. 6 is a partial cross-sectional view illustrating an initial stateof a closing step on an inlet side of a green honeycomb molded bodyaccording to a first embodiment.

FIG. 7 is a cross-sectional view taken along line VII-VII of FIG. 6.

FIG. 8 is a partial cross-sectional view illustrating a middle state ofa closing step in FIG. 6.

FIG. 9 is a cross-sectional view taken along line IX-IX of FIG. 8.

FIG. 10 is a partial cross-sectional view illustrating a final state ofa closing step in FIG. 6.

FIG. 11 is a cross-sectional view taken along line XI-XI of FIG. 10.

FIG. 12 is a partial cross-sectional view illustrating an initial stateof a closing step on an outlet side of a green honeycomb molded bodyaccording to a first embodiment.

FIG. 13 is a cross-sectional view taken along line XIII-XIII of FIG. 12.

FIG. 14 is a partial cross-sectional view illustrating a middle state ofa closing step in FIG. 12.

FIG. 15 is a cross-sectional view taken along line XV-XV of FIG. 14.

FIG. 16 is a partial cross-sectional view illustrating a final state ofa closing step in FIG. 12.

FIG. 17 is a cross-sectional view taken on line XVII-XVII of FIG. 16.

FIG. 18(a) is a diagram illustrating flow of gas that passes throughconventional closed cells.

FIG. 18(b) is a diagram illustrating flow of gas that passes throughclosed cells according to an embodiment of the present invention.

FIG. 19(a) is a perspective view of a green honeycomb molded bodyaccording to a first embodiment before closing.

FIG. 19(b) is a partial enlarged view of FIG. 19(a).

FIG. 20 is a cross-sectional view corresponding to a cross section takenalong line VII-VII of FIG. 6 in a closing step on an inlet side in asecond embodiment.

FIG. 21 is a cross-sectional view corresponding to a cross section takenalong line IX-IX of FIG. 8 in a closing step on an inlet side accordingto a second embodiment.

FIG. 22 is a cross-sectional view corresponding to a cross section takenalong line XI-XI of FIG. 10 in a closing step on an inlet side accordingto a second embodiment.

FIG. 23 is a cross-sectional view corresponding to a cross section takenalong line XIII-XIII of FIG. 12 in a closing step on an outlet sideaccording to a second embodiment.

FIG. 24 is a cross-sectional view corresponding to a cross section takenalong line XV-XV of FIG. 14 in a closing step on an outlet sideaccording to a second embodiment.

FIG. 25 is a cross-sectional view corresponding to a cross section takenalong line XVII-XVII of FIG. 16 in a closing step on an outlet sideaccording to a second embodiment.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be described in detail withreference to the drawings.

First Embodiment Green Honeycomb Molded Body (Octagonal Cells andQuadrangular Cells)

First, a green honeycomb molded body that is an object to be machined inthe first embodiment of the present invention will be described. Asillustrated in FIG. 1(a), a green honeycomb molded body 70 according tothis embodiment is, for example, a cylindrical body that has an uppersurface 71 a, a lower surface 71 b, and a side surface 71 c, and inwhich a plurality of inlet-side octagonal cells 70Octin that areoctagonal through-holes and a plurality of outlet-side quadrangularcells 70Sout that are quadrangular through-holes are open in the uppersurface 71 a and the lower surface 71 b. The inlet-side octagonal cells70Octin and the outlet-side quadrangular cells 70Sout extendsubstantially parallel from the upper surface 71 a to the lower surface71 b along a side surface 71 c. The green honeycomb molded body 70 is anunfired molded body that, by firing later, becomes a porous ceramic.Further, the length of the direction in which the inlet-side octagonalcells 70Octin and the outlet-side quadrangular cells 70Sout in the greenhoneycomb molded body 70 extend is not particularly limited but may be,for example, 40 to 400 mm. The outer diameter of the green honeycombmolded body 70 is also not particularly limited but may be, for example,10 to 360 mm.

As illustrated in FIG. 1(b), in the upper surface 71 a or the lowersurface 71 b, the inlet-side octagonal cells 70Octin having a largeopening area and the outlet-side quadrangular cells 70Sout having asmaller opening area than the inlet-side octagonal cells 70Octin arepartitioned by partition walls 70W. The inlet-side octagonal cells70Octin have an octagonal shape in which the corner portion of thequadrilateral shape is further cut by a straight side. Four outlet-sidequadrangular cells 70Sout are respectively adjacent to portions aroundone inlet-side octagonal cell 70Octin through four partition walls 70Wthat partition four sides except for the corner portion of theinlet-side octagonal cells 70Octin. Four inlet-side octagonal cells70Octin are respectively adjacent to portions around one outlet-sidequadrangular cell 70Sout through four partition walls 70W that partitionrespective sides of the outlet-side quadrangular cells 70Sout. Theinlet-side octagonal cells 70Octin may not have a regular octahedralshape, and the outlet-side quadrangular cells 70Sout may not have aregular square shape. For example, the inlet-side octagonal cells70Octin may have an octagonal shape that is long in one direction, andthe outlet-side quadrangular cells 70Sout may have a rectangular shape.Further, the inlet-side octagonal cells 70Octin may have an octagonalshape in which the corner portion of a parallelogram shape is cut by astraight side, and the outlet-side quadrangular cells 70Sout may have aparallelogram shape.

It should be noted that the outer shape of the green honeycomb moldedbody 70 is not limited to a cylindrical shape and may be an ellipticalcolumn, an angular column (for example, a regular polygonal column suchas a triangular column, a square column, a hexagonal column, or anoctagonal column; or a triangular column, a square column, a hexagonalcolumn, or an octagonal column other than the regular polygonal column)or the like. In this embodiment, a cylindrical shape of the greenhoneycomb molded body 70 will be described.

Such a green honeycomb molded body 70 is produced by extruding a ceramiccomposition with an extruder. In this case, in order to prepare aceramic composition, a powder of an inorganic compound source which is aceramic raw material, an organic binder, a solvent, and, if necessary,additives to be added are provided.

Inorganic compound source powders include powders containing two or moretypes of powders selected from the group consisting of aluminum sourcepowders, magnesium source powders, silicon source powders, and titaniumsource powders; or powders containing one or more types of powdersselected from any one of silicon carbide source powders, silicon nitridesource powders, and aluminum nitride source powders. In order to improveheat resistance and mechanical strength of products, one or more typesof any one of carbon source powders, zirconium source powders,molybdenum source powers, and calcium source powders may be added to theinorganic compound source powder. Including aluminum source powders,magnesium source powders, titanium source powders, and silicon sourcepowders can improve heat resistance. Examples of organic binders includecelluloses such as methylcellulose, carboxylmethylcellulose,hydroxyalkylmethylcellulose, and sodium carboxylmethylcellulose;alcohols such as polyvinyl alcohol; and lignin sulfonic acid salts.Additives include, for example, pore forming agents, lubricating agentsand plasticizers, dispersing agents, and solvents.

The green honeycomb molded body according to this embodiment is producedby mixing the prepared raw materials with a kneader or the like toobtain a raw material mixture, and extruding the raw material mixturethus obtained through an extruder having an outlet opening correspondingto the sectional shape of the partition walls 70W.

(Ultrasonic Closing Machine)

An ultrasonic closing machine in this embodiment will be describedbelow. As illustrated in FIG. 2, an ultrasonic closing machine 300 inthis embodiment includes an ultrasonic signal transmitter 310, anultrasonic oscillator 320, a horn 330, and a closing tool 400. As withthe above ultrasonic cutter 200, the ultrasonic signal transmitter 310transmits electric ultrasonic signals. The ultrasonic oscillator 320converts electric ultrasonic signals supplied from the ultrasonic signaltransmitter 310 to mechanical ultrasonic vibration. The horn 330amplifies an amplitude of the ultrasonic vibration supplied from theultrasonic oscillator 220. The closing tool 400 is vibrated at afrequency of about 20 to 40 kHz by the ultrasonic vibration suppliedfrom the horn 330.

(Closing Tool)

The closing tool in this embodiment will be described below. In thisembodiment, closing is carried out in an identical mode at both endsurfaces of the green honeycomb molded body 70 having the inlet-sideoctagonal cells 70Octin and the outlet-side quadrangular cells 70Sout.First, a closing tool for closing an upper surface 71 a located on anexhaust gas supply side (inlet side) when the green honeycomb moldedbody 70 is applied to a particulate-matter-removing filter such as adiesel particulate filter after firing will be described.

As illustrated in FIG. 3, a closing tool 400 in this embodiment includesa closing surface 401 a for performing closing of the green honeycombmolded body 70; and a support socket 450 in which the end of the greenhoneycomb molded body 70 is fitted. In the closing surface 401 a, aplurality of closing projections 410 a for welding partition walls 70Wto each other and closing the outlet-side quadrangular cells 70Sout areprovided by being arranged at positions corresponding to the inlet-sideoctagonal cells 70Octin and inserted respectively into the inlet-sideoctagonal cells 70Octin. The support socket 450 is formed of acylindrical concave corresponding to the diameter of the green honeycombmolded body 70 to be closed. An inclined surface 451 is provided on theinner periphery of the support socket 450 in such a manner that theinner diameter of the support socket 450 increases with an increase indistance from the closing surface 401 a to facilitate the insertion ofthe end of the green honeycomb molded body 70 into the support socket450.

As illustrated in FIGS. 4 and 5 that are enlarged views of a sitecorresponding to a portion A in the above-described FIG. 3, the closingtool 400 in this embodiment includes closing projections 410 c in aclosing surface 401 c of a closing tool 40 that is identical to that inthe first embodiment. The closing projections 410 c include aquadrangular pyramid-shaped base 416 and a conical tip 412. Thequadrangular pyramid-shaped base 416 is located at a base of the closingprojections 410 c and is projected from the closing surface 401 c. Thequadrangular pyramid-shaped base 416 has a square cone platform shape inwhich a quadrangular pyramid reduced similarly from a quadrangularpyramid having a larger apex angle than the conical tip 412 is removed.The conical tip 412 is located at a position that is a tip of theclosing projections 410 c and above the quadrangular pyramid-shaped base416. The conical tip 412 has a conical shape having a bottom surfacehaving a size corresponding to the upper surface of the quadrangularpyramid-shaped base 416. The apex angle of the conical tip 412 issmaller than the apex angle defined by lateral edges of the square coneplatform of the quadrangular pyramid-shaped base 416.

The quadrangular pyramid-shaped base 416 includes a quadrangular pyramidside surface 417 that is a side surface of the square cone platform; anda roundness chamfering lateral edge 415 on the lateral edge of thesquare cone platform. In the roundness chamfering lateral edge 415,roundness chamfering has been conducted at a prescribed curvature foreach lateral edge of the square cone platform. Further, the valleybetween the quadrangular pyramid-shaped bases 416 in adjacent closingprojections 410 c includes a roundness chamfering valley 414 that is aconcave formed by roundness chamfering at a prescribed curvature.

As illustrated in FIG. 5, in each of the closing projections 410 c,apexes of conical tips 412 are arranged respectively at positionscorresponding to the plurality of inlet-side octagonal cells 70Octin inthe green honeycomb molded body 70. Further, in each of the closingprojections 410 c, the roundness chamfering lateral edge 415 of thequadrangular pyramid-shaped base 416 is arranged in a direction thatabuts against the partition wall 70W. The size of each of thequadrangular pyramid-shaped bases 416 is a size such that a length thatthe roundness chamfering lateral edge 415 projects on the closingsurface 401 c from just above the closing surface 401 c corresponds to alength between the center of the inlet-side octagonal cells 70Octin andthe center of the outlet-side quadrangular cells 70Sout in the greenhoneycomb molded body 70.

It should be noted that when the green honeycomb molded body 70 isapplied to a particulate-matter-removing filter such as a dieselparticulate filter after firing, as with the upper surface 71 a, aclosing tool 400 that has a closing surface 401 c with closingprojections 410 c arranged at positions corresponding to the outlet-sidequadrangular cells 70Sout is used as the closing tool 400 for closingthe lower surface 71 b functioning as an exhaust gas discharge side (anoutlet side).

(Closing Step)

The step of closing the green honeycomb molded body 70 in thisembodiment will be described below. First, in the case where the greenhoneycomb molded body 70 is applied to a particulate-matter-removingfilter such as a diesel particulate filter after firing, the step ofclosing the upper surface 71 a functioning as an exhaust gas supply side(an inlet side) will be described.

As illustrated in FIG. 6, the end on the upper surface 71 a side of thegreen honeycomb molded body 70 is inserted into the support socket 450in the closing tool 400 in the ultrasonic closing machine 300. Theclosing tool 400 is vibrated by ultrasonic vibration from the horn 330.As illustrated in FIG. 7, the tip of the closing projections 410 c inthe closing surface 401 c is inserted into the inlet-side octagonalcells 70Octin. The conical tip 412 of the closing projections 410 c isinserted into the inlet-side octagonal cells 70Octin.

As illustrated in FIG. 8, when the closing projections 410 c are furtherinserted into the inlet-side octagonal cells 70Octin, as illustrated inFIG. 9, the quadrangular pyramid-shaped base 416 of the closingprojections 410 c is inserted into the inlet-side octagonal cells70Octin. The roundness chamfering lateral edges 415 in the quadrangularpyramid-shaped base 416 each abut against the partition walls 70W. Sincethe closing projections 410 c are vibrated by ultrasonic vibration, thepartition walls 70W are liquefied and pressed so as to close theoutlet-side quadrangular cells 70Sout into which the closing projections410 c, that are located at the center of four inlet-side octagonal cells70Octin into which the closing projections 410 c have respectively beeninserted, have not been inserted.

As illustrated in FIG. 10, when the closing projections 410 c arefurther inserted into the inlet-side octagonal cells 70Octin, asillustrated in FIG. 11, the partition walls 70W that have been pressedfrom four directions while being liquefied by the roundness chamferinglateral edge 415 and the quadrangular pyramid side surface 417 in thequadrangular pyramid-shaped base 416 are integrally welded to eachother. The end of the welded partition walls 70W is abutted against theroundness chamfering valley 414 in the closing surface 401 c, and around partition wall joined end 73 is formed in such a state thatroundness chamfering corresponding to the shape of the roundnesschamfering valley 414 has been conducted, thereby completing closing.Thus, in the upper surface 71 a functioning as the exhaust gas supplyside (inlet side), one outlet-side quadrangular cell 70Sout that issurrounded by four inlet-side octagonal cells 70Octin respectivelyadjoining the periphery of one outlet-side quadrangular cell 70Sout withthe partition walls 70W provided between is closed.

On the other hand, when the green honeycomb molded body 70 is applied toa particulate-matter-removing filter such as a diesel particulate filterafter firing, for the step of closing the lower surface 71 b functioningas the exhaust gas discharge side (outlet side), as illustrated in FIG.12, the end on the lower surface 71 b side of the green honeycomb moldedbody 70 is inserted into the support socket 450 in the closing tool 400in the ultrasonic closing machine 300. The closing tool 400 is vibratedby ultrasonic vibration from the horn 330. The tip of the closingprojections 410 c in the closing surface 401 c is inserted into theoutlet-side quadrangular cells 70S out. As illustrated in FIG. 13, theconical tip 412 in the closing projections 410 c is inserted into theoutlet-side quadrangular cells 70Sout.

As illustrated in FIG. 14, when the closing projections 410 c arefurther inserted into the outlet-side quadrangular cells 70Sout, thequadrangular pyramid-shaped base 416 in the closing projections 410 c isinserted into the outlet-side quadrangular cells 70Sout, as illustratedin FIG. 15. Each of the roundness chamfering lateral edges 415 in thequadrangular pyramid-shaped base 416 is abutted against the partitionwalls 70W. Since the closing projections 410 c are vibrated byultrasonic vibration, the partition walls 70W are liquefied and each ispressed so as to close the inlet-side octagonal cells 70Octin into whichthe closing projections 410 c have not been inserted and that arelocated at the center of the four outlet-side quadrangular cells 70Soutinto which the closing projections 410 c have been inserted.

As illustrated in FIG. 16, when the closing projections 410 c arefurther inserted into the outlet-side quadrangular cells 70Sout, asillustrated in FIG. 17, the partition walls 70W that have been pressedfrom four directions while being liquefied by the roundness chamferinglateral edge 415 and the quadrangular pyramid side surface 417 in thequadrangular pyramid-shaped base 416 are integrally welded to eachother. The end of the welded partition walls 70W is abutted against theroundness chamfering valley 414 in the closing surface 401 c, and around partition wall joined end 73 is formed in such a state thatroundness chamfering corresponding to the shape of the roundnesschamfering valley 414 has been conducted, thereby completing closing.Thus, in the lower surface 71 b functioning as the exhaust gas dischargeside (outlet side), one inlet-side octagonal cell 70Octin that issurrounded by four outlet-side quadrangular cells 70Sout respectivelyadjoining the periphery of one inlet-side octagonal cell 70Octin withthe partition walls 70W provided between is closed.

In this embodiment, in the method for producing a honeycomb structure, aplurality of inlet-side octagonal cells 70Octin and a plurality ofoutlet-side quadrangular cells 70Sout that have been mutuallypartitioned by partition walls 70W are open in an upper surface 71 a anda lower surface 71 b of a columnar body. The inlet-side octagonal cells70Octin or the outlet-side quadrangular cells 70Sout are closed byjoining together the partition walls 70W in the green honeycomb moldedbody 70, that become a honeycomb structure by firing, at the uppersurface 71 a and the lower surface 71 b. Thereby, since the cells areclosed by joining the partition walls (cell walls) 70W together, thereis no need to use closing pastes such as in conventional methods.Further, since the cells are closed by welding the cell walls together,when the honeycomb structure is used in a particulate-matter-removingfilter such as a diesel particulate filter, the inlet and the outlet ofexhaust gas flow passages in the end surface can be made larger than anopening area of the through-holes, whereby turbulence of the flow of theexhaust gas at the end surface on the exhaust gas supply side can bereduced and pressure loss can be reduced. As illustrated in FIG. 18(a),when the outlet-side quadrangular cells 70Sout are closed with aconventional closing material 70P, there is a drawback that airresistance is large at the upper surface 71 a functioning as the exhaustgas supply side (inlet side). On the other hand, as illustrated in FIG.18(b), when the outlet-side quadrangular cells 70Sout are closed by theproduction method in this embodiment, since the inlet of the gas flowpassage in the upper surface 71 a is large and the end of the closedpartition walls 70W is tapered, the air resistance can be reduced to avery high extent.

The green honeycomb molded body 70 with a part of through-holes to beclosed has, in the upper surface 71 a or the lower surface 71 b, oneinlet-side octagonal cell 70Octin and four outlet-side quadrangularcells 70Sout that have a smaller opening area than the inlet-sideoctagonal cell 70Octin adjoining around the one inlet-side octagonalcell 70Octin through the partition walls 70W. Accordingly, for example,when the honeycomb structure is applied to a particulate-matter-removingfilter such as a diesel particulate filter, in theparticulate-matter-removing filter, when the inlet-side octagonal cells70Octin having a large opening area are opened while closing theoutlet-side quadrangular cells 70Sout having a small opening area on theinlet side, and when the outlet-side quadrangular cells 70Sout having asmall opening area are opened while closing the inlet-side octagonalcells 70Octin having a large opening area on the outlet side, the inletside becomes wide and the pressure loss in such a state that soot isdeposited can be reduced.

Further, the through-holes having a large opening area are inlet-sideoctagonal cells 70Octin and the through-holes that adjoin around theinlet-side octagonal cells 70Octin and have a small opening area areoutlet-side quadrangular cells 70Sout. Therefore, when the outlet-sidequadrangular cell 70Sout adjoins every other side of the inlet-sideoctagonal cell 70Octin, through-holes having a different size can bearranged in the upper surface 71 a or the lower surface 71 b.

Further, in the upper surface 71 a, the outlet-side quadrangular cells70Sout are closed, and, in the lower surface 71 b, the inlet-sideoctagonal cells 70Octin are closed. Thus, for example, when thehoneycomb structure is applied to a particulate-matter-removing filtersuch as a diesel particulate filter, in the particulate-matter-removingfilter, when the inlet-side octagonal cells 70Octin having a largeopening area are opened while closing the outlet-side quadrangular cells70S out having a small opening area on the inlet side, and when theoutlet-side quadrangular cells 70Sout having a small opening area areopened while closing the inlet-side octagonal cells 70Octin having alarge opening area on the outlet side, the inlet side becomes wide andthe pressure loss in such a state that soot is deposited can be reduced.

When closing projections 410 c in the closing tool 400 are inserted intothe plurality of inlet-side octagonal cells 70Octin or outlet-sidequadrangular cells 70Sout in the green honeycomb molded body 70, thepartition walls 70W are joined together at the upper surface 71 a or thelower surface 71 b and the cells are closed. Thus, the closing of thecells can very easily be carried out.

Further, in the closing of the outlet-side quadrangular cells 70Sout,the outlet-side quadrangular cells 70Sout are closed by insertingclosing projections 410 c in the closing tool 400 including any shape ofa quadrangular pyramid and a quadrangular pyramid platform into theinlet-side octagonal cells 70Octin while allowing the roundnesschamfering lateral edge 415 to abut against each of the partition walls70W that adjoin the roundness chamfering lateral edge 415. Thus, theoutlet-side quadrangular cells 70Sout can be closed easily and reliably.

Further, in the closing of the inlet-side octagonal cells 70Octin, theinlet-side octagonal cells 70Octin are closed by inserting closingprojections 410 c in the closing tool 400 including any shape of aquadrangular pyramid and a quadrangular pyramid platform intothrough-holes, respectively, in the outlet-side quadrangular cells70Sout while allowing the roundness chamfering lateral edge 415 of theclosing projections 410 c to abut against the partition walls 70Wadjacent to the inlet-side octagonal cells 70Octin. Thus, the inlet-sideoctagonal cells 70Octin can be closed easily and reliably.

Second Embodiment Green Honeycomb Molded Body (Rounded QuadrangularCells and Quadrangular Cells)

First, a green honeycomb molded body that is an object to be machined inthe second embodiment of the present invention will be described. Asillustrated in FIG. 19(a), a green honeycomb molded body 70 in thisembodiment is, for example, a cylindrical body that has an upper surface71 a, a lower surface 71 b, and a side surface 71 c and in which aplurality of inlet-side rounded quadrangular cells 70SRin that arerounded quadrangular through-holes with the corner of the quadranglebeing rounded, and outlet-side quadrangular cells 70Sout that arequadrangular through-holes that are the same as those in the firstembodiment are open in the upper surface 71 a and the lower surface 71b. The inlet-side rounded quadrangular cells 70SRin and the outlet-sidequadrangular cells 70Sout extend substantially parallel from the uppersurface 71 a to the lower surface 71 b along the side surface 71 c. Aswith the above-described first embodiment, the green honeycomb moldedbody 70 is an unfired molded body that, by firing later, becomes aporous ceramic and is identical in material and production method tothat in the first embodiment except for the inlet-side roundedquadrangular cells 70SRin. Further, the length of the direction in whichthe inlet-side rounded quadrangular cells 70SRin and the outlet-sidequadrangular cells 70Sout in the green honeycomb molded body 70 extendis not particularly limited but may be, for example, 40 to 400 mm.

As illustrated in FIG. 19(b), in the upper surface 71 a or the lowersurface 71 b, inlet-side rounded quadrangular cells 70SRin having alarge opening area and outlet-side quadrangular cells 70Sout having asmaller opening area than the inlet-side rounded quadrangular cells70SRin are partitioned by partition walls 70W. The inlet-side roundedquadrangular cells 70SRin have a rounded quadrangular shape in which thecorner of the quadrangle has been roundly chamfered. Four outlet-sidequadrangular cells 70Sout adjoin around one inlet-side roundedquadrangular cell 70SRin through respective four partition walls 70Wthat partition the four sides of the inlet-side rounded quadrangularcell 70SRin. Four inlet-side rounded quadrangular cells 70SRin adjoinaround one outlet-side quadrangular cell 70Sout through respective fourpartition walls 70W that partition each side of the outlet-sidequadrangular cells 70Sout. It should be noted that the inlet-siderounded quadrangular cells 70SRin may not be one in which the corner ofa square has been rounded. For example, the inlet-side roundedquadrangular cells 70SRin may have a round quadrangular shape that iselongate in one direction. Alternatively, the inlet-side roundedquadrangular cells 70SRin may have a round quadrangular shape in whichthe corner of a parallelogram has been rounded.

(Closing Step)

The step of closing the green honeycomb molded body 70 in thisembodiment will be described below. In this embodiment, the inlet-siderounded quadrangular cells 70SRin and the outlet-side quadrangular cells70Sout are closed using a closing tool 400 that is the same as that inthe above-described first embodiment. First, the step of closing theupper surface 71 a functioning as an exhaust gas supply side (an inletside) in the case where the green honeycomb molded body 70 is applied toa particulate-matter-removing filter such as a diesel particulate filterafter firing will be described.

As illustrated in FIG. 6, the end on the upper surface 71 a side of thegreen honeycomb molded body 70 is inserted into the support socket 450in the closing tool 400 in the ultrasonic closing machine 300. Theclosing tool 400 is vibrated by ultrasonic vibration from the horn 330.As illustrated in FIG. 20, the tip of the closing projections 410 c inthe closing surface 401 c is inserted into the inlet-side roundedquadrangular cells 70SRin. The conical tip 412 of the closingprojections 410 c is inserted into the inlet-side rounded quadrangularcells 70SRin.

As illustrated in FIG. 8, when the closing projections 410 c are furtherinserted into the inlet-side rounded quadrangular cells 70SRin, asillustrated in FIG. 21, the quadrangular pyramid-shaped base 416 in theclosing projections 410 c are inserted into the inlet-side roundedquadrangular cells 70SRin. The roundness chamfering lateral edges 415 inthe quadrangular pyramid-shaped base 416 each abut against the partitionwalls 70W. Since the closing projections 410 c are vibrated byultrasonic vibration, the partition walls 70W are liquefied and pressedso as to close the outlet-side quadrangular cells 70Sout into which theclosing projections 410 c have not been inserted that are located at thecenter of four inlet-side rounded quadrangular cells 70SRin into whichthe closing projections 410 c have respectively been inserted.

As illustrated in FIG. 10, when the closing projections 410 c arefurther inserted into the inlet-side rounded quadrangular cells 70SRin,as illustrated in FIG. 22, the partition walls 70W that have beenpressed from four directions while being liquefied by the roundnesschamfering lateral edge 415 and the quadrangular pyramid side surface417 in the quadrangular pyramid-shaped base 416 are integrally welded toeach other. The end of the welded partition walls 70W is abutted againstthe roundness chamfering valley 414 in the closing surface 401 c, and around partition wall joined end 73 is formed in such a state thatroundness chamfering corresponding to the shape of the roundnesschamfering valley 414 has been conducted, thereby completing closing.Thus, in the upper surface 71 a functioning as the exhaust supply side(inlet side), one outlet-side quadrangular cell 70Sout that issurrounded by four inlet-side rounded quadrangular cells 70SRinrespectively adjoining the periphery of one outlet-side quadrangularcell 70Sout with the partition walls 70W provided between is closed.

On the other hand, when the green honeycomb molded body 70 is applied toa particulate-matter-removing filter such as a diesel particulate filterafter firing, for the step of closing the lower surface 71 b functioningas the exhaust gas discharge side (outlet side), as illustrated in FIG.12, the end on the lower surface 71 b side of the green honeycomb moldedbody 70 is inserted into the support socket 450 in the closing tool 400in the ultrasonic closing machine 300. The closing tool 400 is vibratedby ultrasonic vibration from the horn 330. The tip of the closingprojections 410 c in the closing surface 401 c are inserted into theoutlet-side quadrangular cells 70Sout. As illustrated in FIG. 23, theconical tip 412 of the closing projections 410 c is inserted into theoutlet-side quadrangular cells 70Sout.

As illustrated in FIG. 14, when the closing projections 410 c arefurther inserted into the outlet-side quadrangular cells 70Sout, thequadrangular pyramid-shaped base 416 in the closing projections 410 c isinserted into the outlet-side quadrangular cells 70Sout, as illustratedin FIG. 24. Each of the roundness chamfering lateral edges 415 in thequadrangular pyramid-shaped base 416 is abutted against the partitionwalls 70W. Since the closing projections 410 c are vibrated byultrasonic vibration, the partition walls 70W are liquefied and each arepressed so as to close the inlet-side rounded quadrangular cells 70SRininto which the closing projections 410 c have not been inserted and thatare located at the center of the four outlet-side quadrangular cells70Sout into which the closing projections 410 c have been inserted.

As illustrated in FIG. 16, when the closing projections 410 c arefurther inserted into the inlet-side octagonal cells 70Octin, asillustrated in FIG. 25, the partition walls 70W that have been pressedfrom four directions while being liquefied by the roundness chamferinglateral edge 415 and the quadrangular pyramid side surface 417 in thequadrangular pyramid-shaped base 416 are integrally welded to eachother. The end of the welded partition walls 70W is abutted against theroundness chamfering valley 414 in the closing surface 401 c, and around partition wall joined end 73 is formed in such a state thatroundness chamfering corresponding to the shape of the roundnesschamfering valley 414 has been conducted, thereby completing closing.Thus, in the lower surface 71 b functioning as the exhaust gas dischargeside (outlet side), one inlet-side rounded quadrangular cell 70SRin thatis surrounded by four outlet-side quadrangular cells 70Sout respectivelyadjoining the periphery of the lower surface 17 b with the partitionwalls 70W provided between is closed.

In this embodiment, the through-holes having a large opening area areinlet-side rounded quadrangular cells 70SRin and the through-holes thatadjoin around the inlet-side rounded quadrangular cells 70SRin and havea small opening area are outlet-side quadrangular cells 70Sout.Therefore, when the outlet-side quadrangular cell 70Sout adjoins everyother side of the inlet-side rounded quadrangular cells 70SRin,through-holes having a different size can be arranged in the uppersurface 71 a or the lower surface 71 b.

It should be noted that the present invention is not limited to theabove embodiments, and various modifications are possible. For example,in the above embodiments, the closed green honeycomb molded body 70 hasbeen closed by welding the partition walls 70W together through theapplication of ultrasonic waves. However, the closed green honeycombmolded body 70 is not limited to this embodiment. For example, theclosed green honeycomb molded body 70 includes a closed green honeycombmolded body 70 that has been closed by contact bonding between partitionwalls 70W without the application of ultrasonic waves. Further, theclosed green honeycomb molded body 70 includes a closed green honeycombmolded body 70 that has been closed by contact bonding between partitionwalls 70W through the application of vibration at a lower frequency thanultrasonic waves, for example, at 1 kHz or less.

INDUSTRIAL APPLICABILITY

The method for producing a honeycomb structure according to one aspectof the present invention can provide a production method in which asealing paste is not needed and which can simply close the end of thehoneycomb structure, and a honeycomb structure produced by the method.

REFERENCE SIGNS LIST

-   70 . . . green honeycomb molded body-   71 a . . . upper surface-   71 b . . . lower surface-   71 c . . . side surface-   70Octin . . . inlet-side octagonal cells-   70Sout . . . outlet-side quadrangular cells-   70SRin . . . inlet-side rounded quadrangular cells-   70W . . . partition walls-   73 . . . round partition wall joined end-   300 . . . ultrasonic closing machine-   310 . . . ultrasonic signal transmitter-   320 . . . ultrasonic oscillator-   330 . . . horn-   400 . . . closing tool-   401 c . . . closing surface-   410 c . . . closing projections-   412 . . . conical tip-   414 . . . roundness chamfering valley-   415 . . . roundness chamfering lateral edge-   416 . . . quadrangular pyramid-shaped base-   417 . . . quadrangular pyramid side surface-   450 . . . support socket-   451 . . . inclined surface

1. A method for producing a honeycomb structure comprising a pluralityof through-holes that open in an end surface of a columnar body and aremutually partitioned by partition walls, a part of the plurality ofthrough-holes having been closed, the method comprising: a closing stepof closing a part of the through-holes by joining the partition walls ina green honeycomb molded body together at the end surface, wherein thegreen honeycomb molded body in which a part of the through-holes areclosed at the closing step includes, at the end surface, one firstthrough-hole and four second through-holes that have a smaller openingarea than the first through hole and adjoin around the one firstthrough-hole with the partition walls provided therebetween.
 2. Themethod for producing a honeycomb structure according to claim 1, whereinthe first through-hole is octagonal and the second through-hole isquadrangular.
 3. The method for producing a honeycomb structureaccording to claim 1, wherein the first through-hole has a roundquadrangular shape with a corner of the quadrangle being rounded, andthe second through-hole has a quadrangular shape.
 4. The method forproducing a honeycomb structure according to claim 1, wherein, at theclosing step, the second through-hole is closed at one of the endsurfaces, and the first through-hole is closed at another end surface.5. The method for producing a honeycomb structure according to claim 1,wherein, at the closing step, a closing tool is inserted into a part ofthe plurality of through-holes in the green honeycomb molded body tojoin the partition walls together at the end surface to close thethrough-holes.
 6. The method for producing a honeycomb structureaccording to claim 5, wherein, at the closing step, in closing thesecond through-holes, the closing tool including any one shape of aquadrangular pyramid and a quadrangular pyramid platform is insertedinto the first through-hole while allowing a lateral edge of the closingtool to abut against each of the partition walls that adjoin the secondthrough-holes to close the second through-holes.
 7. The method forproducing a honeycomb structure according to claim 5, wherein, at theclosing step, in closing the first through-hole, the closing toolincluding any one shape of a quadrangular pyramid and a quadrangularpyramid platform is inserted into each of the second through-holes whileallowing a lateral edge of the closing tool to abut against thepartition walls that adjoin the first through-hole to close the firstthrough-hole.
 8. A honeycomb structure produced by the method accordingto claim 1.